In Project 4, we will test the hypotheses that (i) Nox2-dependent oxidant signaling activates Src kinas dependent ICAM-1-phosphorylation and thereby the recruitment of PMNs in the pulmonary circulation, and that (ii) Src phosphorylation of ICAM-1 in turn protracts Src activation and phosphorylation of caveolin-1 and dynamin-2, thereby triggering caveolae-mediated transcytosis of albumin and endothelial hyper-permeability. These studies will address the following Specific Aims: (1) role of PI3-kinase, PKC zeta, Nox2, and Src signaling, and of Akt phosphorylation of filamin A in the mechanism of ICAM-1 phosphorylation, clustering, and rapid increase in ICAM-1 binding affinity in lung microvascular endothelial cells and PMN uptake in lungs; (2) role of phospho-ICAM-1 in recruitment of SHP2 and protracting Src activation and thereby caveolin-1 and dynamin-2 activation, and thus stimulating caveolae-mediated transcytosis and hyper-permeability of albumin. Project 4 will delineate the signaling mechanisms mediating the post-translational modification of ICAM-1 in pulmonary microvessel endothelial cells using imaging, cell biology, biochemical, and physiological approaches. We will thereby establish how endothelial cell ICAM-1 shifts to a high-affinity state and promotes PMN adhesion and sequestration and also induces caveolae-mediated hyper-permeability via the transcytosis of albumin. These studies it is hoped will lead to a new understanding of the early PMN-mediated lung inflammatory response and its coupling to lung vascular hyper-permeability. Identification of the key signaling hubs of ICAM-1-mediated endothelial adhesivity and activation of the caveolae-mediated albumin transport pathway is likely to provide novel therapeutic targets directed against inflammatory lung injury.